Improved Production of β-Galactosidase from the Mutated Aspergillus sp. on Deproteinized Cheese Whey

Aspergillus sp. was isolated from the soil near the dairy region, Anand, Gujarat and screened for β-galactosidase production using minimal nutrient salt (MNS) medium with 0.004% 5-bromo-4-chloro-3-indolyl b-D-galactoside (x-Gal) with 2% lactose and deproteinized cheese whey agar. Using wild type strain, β-galactosidase production was carried out on deproteinized cheese whey medium with varying lactose concentrations. Maximum β-galactosidase was 49 specific activity (U mg^-1 protein: 1 U is equivalent to 1nM o-nitrophenol produced min^-1) obtained after 72 hours of incubation at 1.5% lactose content using deproteinized cheese whey medium. To improve the production of β-galactosidase, two chemical mutagens viz., ethyl methane sulfonate (EMS) and hypoxyl amine (HA) were used at different concentrations. The mutants were screened on the basis of development of blue colour on MNS agar containing x-Gal after 72 hrs incubation at 30°C whereas wild type strain showed the blue colour at 120 hrs incubation at 30°C. Both the mutants, Aspergillus sp. EMS and Aspergillus sp. HA were also grown on the deproteinized cheese whey medium with varying lactose concentrations for β-galactosidase production. Aspergillus sp. EMS and Aspergillus sp. HA showed 2 and 2.47 fold more β-galactosidase production compared to wild type strain after 72 hours of incubation at 1.5% lactose content, respectively.